Marking devices are used for producing ground markings as are used, for example, for defining playing fields and sports fields. The marking devices have an outlet for marking substance and are generally formed as mobile marking trucks. Before the beginning of the actual marking activity, the field or the lines and/or areas to be marked must be staked out in a defined manner. For example, it is known that the marking region can be defined for this purpose by optical guide beams. Thereafter, an operator guides or drives the marking truck, emitting marking substance, along the guide beams.
Such a system is described, for example, in WO 2006/013386. A beam having fan-shaped geometry and elliptical beam cross-section is produced by a laser diode and an optical system. This beam is emitted for defining one side of a sports field. The marking truck used for applying the marking substance has a detector for the laser radiation, the position of the marking truck relative to the vertically oriented beam being displayed. The user of the truck can guide the latter on the basis of the laser fan as a guide beam.
The laser fan defines a reference plane, relative to which the marking is effected.
DE 40 13 950 A1 discloses a solution in which the guide line is formed by a laser beam. In trade fair halls and on parking areas and playgrounds, a vehicle having a firmly mounted application element is set to move automatically along the laser beam and to apply markings to the ground area according to a specifiable marking programme, depending on the distance covered. The distance covered is determined by detecting the revolutions of a measuring wheel.
The laser guide beam is aligned from the first end of the guide line by means of an adjustable holder with an adjusting plate arranged at the second end of the guide line. After the alignment of the laser beam, a vehicle having a receiver is guided along the beam. The receiver uses a two-dimensional array of photodiodes to determine the deviation of the vehicle from the guide beam. According to the detected lateral deviation, a corrective steering movement of the vehicle is triggered.
In order to be able to dispense with the complicated vehicle control, the European Patent Application with the application number EP 06101449.4 describes a solution in which the attitude of the application element relative to the vehicle can be laterally adjusted by the holder. A receiver firmly connected to the application element detects a deviation of the attitude of the application element from the guide beam, the inclination of the vehicle additionally being measured. The deviation is compensated with a lateral displacement of the application element relative to the vehicle by the holder. To ensure that the vehicle does not deviate from the guide line to such an extent that the compensation by the holder is no longer sufficient, reference is also made to the necessary course correction of the vehicle.
Vertical irregularities of a playing field might result in the laser beam impinging vertically above or below the receiver. In order to avoid a signal loss associated therewith, a laser beam expanded or extended vertically in a fan-like manner is used as a signal beam, it being possible, for example, for the opening angle to be about 1 to 2 degrees.
U.S. Pat. No. 5,613,442 discloses a solution for correcting the lines of tracks. An optical reference beam is detected by a position-sensitive receiver arranged on a railway vehicle. According to the detected line of the reference beam, the line of the track is adjusted by a work element. The inclination is detected by means of a tilt sensor and the longitudinal position of the railway vehicle is detected by means of an odometer. If the rail rises or falls slightly, a reference beam extended vertically in a fan-like manner is used.
For expanding a laser beam in one direction, a concave cylindrical lens is used in DE 197 33 491 A1 and a convex cylindrical lens in U.S. Pat. No. 6,796,040. In the beam extended in a fan-like manner, the luminous intensity decreases with the increasing beam width or increasing distance. At distances with an intensity which is too low, the receiver cannot determine a position signal.
The European Patent Application with the application number EP 05108174.3 describes a reference beam generator for guiding a marking truck for ground markings. This has a support element which can be positioned in a defined manner relative to the Earth's surface, a laser diode and beam guidance means for the emission of the radiation to at least one reference target, the radiation being emitted with an asymmetrical beam cross-section, in particular in a fan-like manner, and the beam guidance means being adjustable in a defined manner relative to the support element. An alignment of the radiation with the reference target can be effected by an optical detection component for detecting and providing the radiation reflected by the reference target, in particular a telescope.
In order to define a reference plane in the case of these known systems, the radiation is therefore emitted in a fan-like manner so that a plane is defined in space by the beam cross-section and the direction of propagation. However, as a result of the fan-like configuration or the elliptical beam cross-section resulting therefrom, the intensity of the radiation which is received or can be received by the detector decreases in comparison with a small beam cross-section which is not fan-like. This reduction of the received intensity by beam divergence is evident in particular in the case of relatively large distances. The maximum beam intensity is generally limited by technical circumstances, such as, for example, the maximum power of an individual laser diode, or other circumstances, such as, for example, by laser protection requirements.
The disadvantage of the known solutions is that asymmetry of the beam cross-section must be produced for producing the reference plane, with the result that the intensity of the radiation decreases so that, depending on the distance, a position signal can often no longer be determined. If on the other hand the beam cross-section is kept small, for example, the orientation of the plane can no longer be determined or cannot be determined sufficiently accurately or the laser beam no longer impinges on the receiver or does so only with a very small part of the beam cross-section.